P H Y S I C A L R E V I E W V O L U M E 9 3 , N U M B E R 1 J A N U A R Y 1 , 1 9 5 4

Isotope Shift in the 5sCe II Spectrum*

HACK ARROE Department of Physics, University of Wisconsin, Madison, Wisconsin

(Received September 30, 1953)

The spectrum of Ce n from enriched samples of Ce136 and Ce138 has been studied and compared with the same spectrum from natural Ce. Only a negligible isotope shift, certainly less than 6 percent of that between the isotopes with 82 and 84 neutrons, has been found between the isotopes with 78, 80, and 82 neutrons.

THE isotope shift between Ce140 and Ce142 has been measured by Brix and Frank1 in some of the

lines 4/26s4#, 2H, *F-4f26p*I°, AH°, T , 4G°. An attempt was made by Murakawa and Ross2 to measure a shift between Ce138 and Ce140 in the 4f26s4H9,2

— 4f26p4I°9/2 line by using an enriched (4.4 percent) sample of Ce138. Murakawa and Ross estimated an upper limit of this shift at about the half of the Ce140—Ce142 shift, which was found by Brix and Frank to be 0.054±0.0Q3K,3 with the Ce142 towards lower frequency.

A new attempt has been made to measure not only the Ce138-Ce140 shift, but also the Ce136-Ce140 shift, in the lines where Brix and Frank measured the shift between Ce140 and Ce142. Enriched samples4 of Ce138

(13.1 percent) and Ce136 (first 22.3 percent, later 30 percent) were available.

The experimental setup consisted of 3 parallel hollow cathode tubes5 and a modified Steinheil three-prism spec-

* Supported by the U. S. Office of Naval Research. 1 P. Brix and H. Kopfermann, Z. Physik 127, 289 (1950). 2 K. Murakawa and J. S. Ross, Phys. Rev. 83, 1272 (1951). 3 lK(kayser)^l cm"1, following a recommendation of the

international Joint Commission for Spectroscopy [see J. Opt. Soc. Am. 43, 410 (1953)].

4 Produced by the F-12 plant, Carbide and Carbon Chemicals Corporation, and obtained by allocation from the U. S. Atomic Energy Commission.

6 H . Arroe and J. E. Mack, J. Opt. Soc. Am. 40, 3S6 (1950).

trograph (designed and built by Mr. George Streander at Wisconsin) with a Perot-Fabry interferometer in the parallel beam between the collimator and the prisms. The spacers used in the interferometer had the sizes: 15, 18, 19, 20, 25, 27, 30, and 40 mm. The coating on the plates was silver in most of the exposures and an aluminum-magnesium alloy in the others. The reflec­tivity exceeded 90 percent.

The shift between Ce140 and Ce142 could be measured in all the lines with all three samples and the value agrees with the value found by Brix and Frank. It was, however, impossible to find any structure from the Ce138

and Ce136 isotopes, which lines seem to coincide with the Ce140 lines. Not even a line broadening was detected. A quantitative measurement of the lines gave the following values for the shifts:

Ce136-Ce140: 0.0003=b0.0032K (33 measurements),

Ce138-Ce140: 0.0002±0.0035K (12 measurements),

with the lighter isotopes in each case towards higher frequency. The uncertainty includes the largest devi­ation from the average.

The author wishes to express his sincere appreciation to Dr. J. E. Mack for his continued interest in the experiment.

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